The present invention concerns a valve assembly, in particular for a pressure washer.
In order to remove dirt and/or sediment from bodies or machinery in general, it is known to use high pressure washers comprising a delivery gun that can be provided with various accessories, and a volumetric pump connected to an electric motor and which sends a flow of water at a predetermined operating pressure to the gun. Generally, between the pump and the delivery gun are interposed a thermal installation provided with a heater in order to increase, where necessary, the temperature of the water delivered by the pump to a desired level, a safety valve for releasing any pressure surges that may occur within the tubing, and a by-pass valve.
In known pressure washing machines, the by-pass valve usually performs the dual function of discharging water delivered by the pump when the delivery of water from the gun ceases, that is, when the trigger of the gun is released, and of controlling the deactivation of the electric motor and heater when it is switched to a by-pass condition.
The by-pass valves usually used comprise an inlet opening connected to the pump, a delivery mouth opening connected to the gun via a unidirectional valve, a discharge opening, and a shutter element interposed between the inlet and discharge openings. The shutter element is held in a closed position by the discharge opening during the delivery of water through the gun, and is moved to an open or by-pass position, in which the inlet and discharge openings are in communication with each other, by a hydraulic command when the water pressure in the delivery opening reaches a predetermined threshold value on releasing the trigger of the gun. When in its open position, the shutter element stops the motor and any possible heating, thereby inhibiting the delivery of water by the pump.
The use of by-pass valves of the type described above, and the manner of control thereof means that the known pressure washers are unsatisfactory, both from a functional point of view, and as regards their service life.
This is essentially due to the fact that maintaining the by-pass valve in its by-pass condition is dependent on the pressure in the delivery opening remaining strictly constant. However, such a condition does not occur in reality, as the pressure in the delivery opening is never constant but varies continuously since small losses of fluid occur in all known pressure washers, and there is always some fluid leakage through the gun when the trigger thereof is released. In some cases, this leakage is inevitable, especially after a relatively long period of use of the gun while, in other cases, they must necessarily be provided for, for example, in order to avoid the fluid present in the circuit freezing when the machine operates at low temperatures. This therefore means that even when the trigger is released, the shutter element returns automatically to the closed condition when there is no pressure control as described above, with the consequent reactivation of the motor and the heater for a relatively short time which, in any case, is sufficient to raise the pressure in the delivery opening to the threshold value and return the shutter element to its open position. It is, therefore, clear that when the trigger is released, the machine operates in an unstable regime which is detrimental both for the pump and the heater, but especially for the motor which not only is forced to operate in a stop-go manner, but starting the motor is also associated with extremely high loads due to the presence of fluid at high pressure in the delivery opening, and this significantly reduces its expected service life.